Well, I have a different question that kinda goes along here. If you are in a
switched environment, i.e. dedicated bandwidth per port, how can you have a collision
at all? To me it seems (and Radia Perlmann touches on this in her book but doesn't
give any explanation) that if there is no chance for a collision (switched
environment) then why a distance limitation? I'm sure there are some other physics
factors that would limit distance but would they be the same as the distance required
to detect a collision?
Steve
------Original Message------
From: "Randy Witt" <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Sent: July 27, 2000 1:53:55 PM GMT
Subject: CCDA question-512 bit times
I have a question regarding the round-trip propagation delay on an Ethernet network.
Page 123 of the Cisco Press "Designing Cisco Networks" book states:
"The most significant design rule for Ethernet is that the round-trip propagation
delay in one collision domain must not exceed 512 bit times, which is a requirement
for collision detection to work correctly."
With 100Mbps Ethernet, the maximum round-trip delay would be 5.12 seconds, resulting
in a distance limitation of 205 meters.
I currently oversee a large flat network covering several miles in diameter. All of
the links between buildings are single-mode fiber links. No routing is involved,
everything is switched - one large broadcast domain.
How does the 512 bit time rule apply to fiber optic cabling? I see on page 127 of the
same book that the Round trip delay in bit times per meter for Cat5 cable is 1.112,
whereas Fiber-optic cable it's 1.0.
I guess I'm having difficulty understanding how fiber can overcome the 512 bit-time
rule and can have a much longer distance.
I do realize that this is not exactly a Cisco question, though covered on the DCN/CCDA
material. If someone could kindly refer me to any material that covers this topic,
I'd appreciate it.
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Steve Brokaw, MCSE CCNA
Sprint Enterprise Network Services
[EMAIL PROTECTED]
[EMAIL PROTECTED] (pager)
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